Constant plate current electron tube



March 10, 1959 e. R. BELLETT 2,877,331

CONSTANT PLATE CURRENT ELECTRON TUBE Filed March 31, 1955 IN VEN TOR. fidi'fi 18.5! 1 77 United States Patent Patented Mar. 10, 1959 2,877,381 CONSTANT PLATE CURRENT ELECTRON TUBE George R. Bellett, Mill Valley, Calif.

Application March 31, 1955, Serial No. 498,295 5 Claims. 01. 315-55 especially to grid controlled tube apparatus for voltage or current regulation purposes.

A principal object of the' invention relates'to ;a novel regulator tube of the thermionic or heated emitter kind,,

and having as an integral element thereof a pyro-voltaic orthermoelectric device which is energized directlyby the temperature of such emitter thereby to control the space current fromv the emitter to another electrode in the tube.

1 A feature of the invention relates to a grid controlled electron tube having a heatable electrode whose temperature determines the space current flow through the tube, and also having a pyro-voltaic generator or thermoelectric couple to control the bias on the grid of the tube and thereby to stabilize the said space current over a relatively Wide range of temperature change of said heatable electrode.

Another feature relates to an electron tube having a thermionic cathode, a control grid, and an output electrode, in conjunction with a thermocouple device mounted in close proximity to a localized region of the cathode and directly connected to the grid to stabilize the output current of the tube.

A further feature relates to the novel organization, arrangement, and relative location and interconnection of parts which cooperate to provide a novel current or voltage regulator tube apparatus of the grid controlled kind.

Other features and advantages will appear as the ensuing specification proceeds.

The invention is not limited to any particular kind or type of grid controlled tube, but is capable of use with any tube having a heatable emissive electrode such as a cathode, cooperating with at least one control grid between the cathode and anode. Consequently, the single figure of the drawing represents any such tube in schematic form. Thus, the tube may comprise an enclosing bulb or envelope within which is enclosed any well known form of radio tube mount comprising for example the heatable filamentary cathode emitter 11, the control grid 12, and the plate or anode 13. These electrodes, which by way of example constitute a triode, are suitably supported within the envelope 10 and each of the electrodes is provided with respective lead-ins sealed vacuum-tight through the wall of the envelope 10 so as to apply the requisite potentials externally thereto. Merely for purposes of illustration, the filamentary cathode 11 is shown as being connected to a battery 14 through an adjustable resistor 15 to control the predetermined normal emission temperature for the filament 11. Likewise the plate or anode 13 is connected through a suitable load device or circuit 16 and to a suitable source 17 of direct current plate power supply. In accordance with well known operation, the positive terminal of source 17 is connected through the load 16 of the anode 13, and the negative terminal of that source is connected to the nega- This invention relates to regulator tubes and more;

. electron tubes.

The control grid 12 is returned to the negative terminal of source 14 through a suitable resistor 18, and in accordance with the invention this resistor is connected in series with a pyro-voltaic generator device or thermoelectric couple 19. This device is illustrated schematically in the drawing and is preferably constituted of a thermopile of relatively small size, which however is mounted in close proximity to'a. localized portion of the heated cathode 11. Itwill be understood, of course, that the device 19 is insulatingly mounted byany suitable spacer and insulator means with respect'to the cathode 11, and the terminals of device 19 are connected to respective leadin members sealed through the wall of envelope 10 so as to connect the device 19 in the desired electrical manner withrespect to the resistor 18.

While the invention is not limited to the mounting of the device 19 adjacent any particular region of the cath-' device 1 9- is constituted of any well known thermoelectric couple or thermopile. Each of these thermocouples may be constituted of any well known thermoelectric elements. Preferably, in order to reduce the cost, these elements may consist of inexpensive elements such as copper and iron, the hot junctions of which are located adjacent the heated filament 11 and the cold junctions of which are connected to the respective lead-ins. As is well known, such a thermocouple produces respective positive and negative potentials at the terminals of the thermocouple in accordance with the temperature of the hot junction. In accordance with the invention, the negative terminal of the thermocouple or thermopile is connected through the resistor 18 to the control grid 12, while the positive terminal of the thermocouple or thermopile is connected to the negative tenninal of the cathode 11.

It is clear, therefore, that the thermoelectric voltage, which is a direct current voltage generated by reason of the temperature of the cathode 11, applies a negative direct current bias through the resistor 18 to the control grid 12. The net negative bias on the grid 12 is therefore a function of the initial adjustment of the resistor 15 and the thermoelectric voltage from the device 19. Thus, the net negative bias on the control grid 12 can be set to correspond to any predetermined temperature of the cathode 11, or in other words to any predetermined seting of the heating current flowing through the cathode. Consequently, the amount of space current flowing between the cathode and anode will also be determined by this net negative bias. Likewise the voltage developed across the load 16 will likewise be so determined.

If, for example, the temperature of the cathode 11 should drop below its normal predesigned value the thermoelectric voltage from the device 19 will likewise drop so that the negative bias on grid 12 will be reduced and will permit an increase in the space pensate for the drop the other hand, the net negative current to comin any thermocouple is a function of the difference between the hot and cold junctions.

While the invention has been described in connection with a tube having a cathode of the heated filamentary type, it will be understood, of course, that this cathode may be of any other well known type, such for example as a so-called indirectly heated cathode wherein the heating element is electrically separate from the emitter surface which is heated thereby.

What is claimed is:

1. Electron discharge tube apparatus comprising, an enclosing envelope containing a heatable emitter, an output electrode, and at least one control grid for determining the output current from the tube, a conductive electrical connection between the emitter and grid to determine the bias on the grid with respect to the emitter, and a pyro-voltaic generator device mounted in close proximity to a localized region of said emitter but out of electrical contact therewith, said generator constituting part of said electrical connection to determine said bias.

2. Electron discharge tube apparatus comprising, an enclosing envelope containing a heatable cathode, an output electrode, and at least one control grid for determining the output current from the tube, a thermoelectric device which is mounted within the envelope in heat transfer relation with said cathode, and means connecting said device between the control grid and the cathode to determine the negative bias on said grid and thereby automatically stabilizing the said output current.

3. Electron discharge tube apparatus comprising,

enclosing envelope containing a heatable cathode, an output electrode, and atleast one control electrode for determining the output current f-rom the tube, a voltage generating thermocouple mounted within the tube having a hot junction thereof adjacent to the cathode but out of electrical contact therewith, the cold junction of said thermocouple being connected to the grid of said tube and to the cathode of said tube to stabilize the said output current by reason of the voltage generated by said thermocouple.

4. Electron discharge tube apparatus according to claim 3 in which said cathode is in the form of a bighted filamentary heated member, and said thermocouple is mounted within the tube with the hot junction in close proximity to the hight' of said filament.

5. Electron discharge tube apparatus according to claim 3 in which adjustable means is provided externally of the tube to adjust the normal temperature of the oathode, and said thermocouple is connected between-the cathode and control grid in series with a resistor.

References Cited in the file of this patent UNITED STATES. PATENTS 1,693,258 Spaeth NOV. 27, 1928; 1,809,475 Dowler June 9, 1931 1 ,905,841 Forney Apr. 25, 1933'- 2,058,829 ROthe Oct. 2,7, 1936; 2,144,509 Renatus Tan. 1 7, 1939 

